In the foundry practice, core-shooting machines have been known for many years. For casting molded components, foundry cores or molds are mostly made in separate parts, combined, and joined to one another to a casting mold. An essential part of the core shooting machines are the so-called core-shooting heads with ejector plates accommodating the shooting nozzles. It has been common practice to fill the mold-core material, in particular core sand, i.e. quartz sand already mixed or coated with binders, into the core-shooting heads under consideration, and thence to blow or shoot it under a very high air pressure through the nozzles arranged in the ejector plate into the respective molds.
In practice, the core shooting heads are filled with core sand almost completely, it further having been common practice to fill the core-shooting heads regardless of the volume of core sand needed in the respective molds. As a result of filling the core-shooting heads to an always considerable extent, the pressure required for the shooting is extremely high. This pressure is normally between four and six bar. This extremely high pressure is required in particular for the reason that a considerable quantity of core sand is present between the shooting nozzles and the source of inflow of the compressed air used for the shooting operation. To accelerate the sand particles through the nozzle, it is necessary to blow the compressed air through the entire volume of sand in the core-shooting head. Added to this is an always uneven distribution of the core sand in the core-shooting heads. As a result, the pressure required for a continuous shooting operation has again to be very high.
Core-shooting under high air pressures which have so far been absolutely necessary, is however extremely problematic in practice, since the sand exiting from the shooting nozzles impacts always upon the walls of the mold to be filled, and has there an extremely abrasive effect. In other words, the shooting nozzles operate in the meaning of a sand blasting gun, so that the core sand exiting under a high pressure damages the mold to be filled successively, or changes same in its geometry. A further disadvantage of core-shooting under high air pressures may be seen in that already when the core sand is shot into the mold, the high air pressures lead to compressions of the core sand in the region of the injection or shooting. Consequently, in particular in the case of complicated geometries, a form-locking filling of the mold is impeded, or at least considerable density gradients develop.
Furthermore, as a result of the high air pressures and the resultant heavy impact of the sand upon the walls of the respective mold, a binder adhering to the sand is downright blown off or separated, and last not least an uneven distribution of sand and binder develops as a result of the density differences between sand and binder. Gases which are liberated at high temperatures from binder concentrations, prevent again a uniform compression or the formation of a flawless core.
Finally, in the known core-shooting practice a serious problem lies in that, regardless of the volumes of cores to be shot, the core-shooting heads are always filled to the same level. As a consequence, it is necessary, even when the dimensions of the cores to be shot are very small, to blast the compressed air required for the shooting through the core sand deposit stored in the core-shooting head, or to accelerate the core sand particles directly adjacent to the shooting nozzles. On the one hand, the large dimensions of the core-shooting heads required for the shooting of large cores, and on the other hand the considerable volume of core sand to be penetrated by the compressed air, however, absolutely necessitate the high pressures previously represented to be extremely disadvantageous.
It is therefore the object of the present invention to describe a device and a method of filling core-shooting heads and mold-core materials, which allow for purposes or reducing the compressed air pressures required for the shooting of cores, to fill the core-shooting head in portions, and yet evenly, with a mold-core material.